Generally, muscular function shuts down because of trauma and/or injury inflicted to the muscle, ligaments, joints and/or bones. For instance, the front and outside of the lower leg includes the shin, the top of the foot and the outside of the ankle up to the knee. It is home to the tibialis anterior, the tibialis posterior, the extensor digitorum, and the peroneal muscles. It is also a common area for overuse injuries in the form of tendonitis, muscle strains/sprains and spasms, the most popular of which is “shin splints.”
In normal walking gait, these muscles are responsible for lowering the foot to the ground. The front muscles or dorsiflexors have a primary function to pull the toes and ankle upwardly, and to slowly lower the foot to the ground from heel to toe. The outer muscles have a primary function to evert the foot or tilt the foot out to the side away from the body, and to slowly lower the foot to the ground from the outside of the heel, over the arch and onto the big toe. The term “evert” means to turn a structure away from a normal position (such as, to turn the structure outward). As a person moves through push off, these muscles rely on elastic recoil to pull the toes and ankle up for clearance through the swing phase. This reduces a large amount of the stress on these muscles and allows them to use their full strength for shock absorption at heel strike. However, if push off is decreased in any way (as a result of over pronation, high arches, tight calves, for instance), these muscles must then work overtime to not only pull the toes/ankle upwardly so that the person does not trip over them and but also to slowly lower the foot to the ground upon heel strike. Over time, these muscles may become overworked and can break down and/or become deactivated (unable to actively contract when required to do just so).
The shin is the common name for the front of the lower leg bone (tibia) and its associated muscles and tendons. While muscles on the front of the leg (primarily the tibialis anterior) serve to point the toes and foot upwards (dorsiflexion), the tibialis posterior serves to point the toes and foot downwards (plantar flexion). Anterior shin splints exist on the front of the lower leg, while posterior shin splints present pain along the inside edge of the lower leg in the tibialis posterior tendon. The role of the tibialis posterior is to support the arch as the body moves over the foot during the gait cycle. In medical terms, posterior shin splints are known as posterior tibial tendon dysfunction, or PTTD. PTTD describes a weakening of the tibialis posterior tendon, and in severe cases may result in a rupture of the tendon. Posterior shin splints may be considered the onset of PTTD. If the forces (singular or cumulative) applied to the tendon are greater than what the tendon can bear in its current state, inflammation and micro-trauma will result. Excessive pronation, changes of shoe or running surface, compensations for previous injuries or poor mechanics, and general overuse are all common causes of posterior shin splints. Other causes include muscle imbalances in the leg, flat feet or fallen arches, and activity that may require frequent and abrupt changes in direction (which are symptoms of muscular dysfunction).
The posterior tibialis is often overlooked. It is a major source of shin splints and plantar fasciitis. Injury to the anterior tibialis is called a shin splint (also known as tibial-stress syndrome). The shin splint is a repetitive overuse injury caused by tight calves and ankles, improper footwear, or abnormal mechanics (i.e. running form or cycling form of a person). Posterior shin splint pain is specific to the medial ankle, just behind the medial malleolus and along the lower and inner shin. Note that this location is different from anterior shin splints. Pain (at an area) may be felt to the touch, and the area having the pain (generally) may not exhibit visible swelling. The pain can range anywhere from faint and annoying to sharp and debilitating. When the condition worsens, bumps can be felt along the area and represent major inflammation and distortions in the underlying fascia. At the onset, pain is generally felt at the beginning of activity and dissipates over a relatively short period of time. As the condition worsens, the pain is constant and may result in stress fractures.